Their mass walkout weeks ago over a government plan to boost medical school admissions has left hospitals turning away patients and delaying operations.
Now the trainees are getting support from medical professors, who submitted their resignations en masse to back the strike.
Here's Kim Chang-soo, the president of the Medical Professors Association of Korea:
"It is clear that increasing medical school admissions will not only ruin medical school education but cause our country's healthcare system to collapse."
Kim said some professors are cutting their hours in outpatient treatment to focus on emergency and severely ill patients.
He did not say how many put in their resignations.
But he warned that more will come if the government goes ahead with punishments for the striking trainees.
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About 70% of the country's junior doctors walked off the job en masse on February 20.
That's about 9,000 people.
They're asking for better work conditions and pay.
And they're angry that the government is focusing instead on raising the number of students admitted each year to medical school from 2025.
The government says the move is vital to tackle a shortage of doctors in one of the world's fastest-ageing societies.
President Yoon Suk Yeol has vowed to stand firm on boosting the medical student headcount.
Officials have threatened to suspend the licenses of the doctors who have left their posts.
But on Sunday, Yoon appeared to soften his stance and urged the country's prime minister to seek "flexible measures" in dealing with the suspension.
Yoon's office said he also ordered the prime minister to form a "constructive consultative body" to speak with all medical professionals.
